The proposed invention relates to articles of footwear. More specifically, the invention relates to a sole system that integrates an eccentric toe-off cam lever (“cam lever”) into footwear. The integrated cam lever allows for both plantarflexion and dorsiflexion; provides a mechanical advantage through articulation of the forefoot to stimulate an upward plantar moment force during toe-off; and increases the distance per step without altering the stride pattern.
During the running or walking gait (“gait”), the foot strikes the ground and rolls forward. The foot does not strike the ground flat, but forms contact with the ground on either the heel or toe. During this motion, the foot travels through heel strike, mid-stance, and toe-off.
Attempts have been made to increase the distance per step by selected modification of the natural biomechanics of the gait. One example of an alteration includes taking longer strides. “Over striding” involves placing the lead foot down on its heel and in front of the body; resulting in a breaking effect, both interrupting natural forward momentum and increasing ground contact time.
Mechanical adaptations have also been used to alter the gait by selected modifications to running shoes. The selected modifications alter the locomotion, bio-mechanic posture, and gait of the wearer. Unshod runners typically alter their running gait to a forefoot striking pattern, to avoid the harsh impact of heel first striking Shoe designs attempt to compensate for this by increasing the width, thickness, and impact absorbing properties of the heel of the shoe. As a result, shod runners may tend to heel strike.
At faster running paces, and during sprinting, the heel strike phase may be omitted, as the runner tends to elevate to the toes. Thick heels are not conducive to the cadence and biomechanics of the toe-striking pattern. Specifically, the thicker heels decrease the plantarflexion and dorsiflexion of the ankle, and relocate the center-of-gravity towards the rear of the shoe. In addition, the mechanics resulting from the natural anatomical design of the human foot is ignored, due to the ankles and lower leg muscles performing much of the bio-mechanical assistance during heel strike, mid-stance, and toe-off.
Attempts have been made to increase the orthotic benefits and/or cushioning of shoe designs. See for example, U.S. Pat. Nos. 5,572,805, 5,918,338, and 7,779,557. Additional attempts have been made to use the downward force of the runner. See for example: U.S. Pat. Nos. 4,689,898, 5,528,842, 6,928,756, 6,944,972, 7,337,559, and 7,788,824; and U.S. Patent Application Publication Nos. 2003/0188455, 2005/0268489, 2006/0174515, and 2010/0031530. Further attempts have been made to allow articulation of individual toes. See for example, U.S. Pat. Nos. 5,384,973, and 7,805,860. However, each of these designs suffers from one or more disadvantages. Therefore, a need arises for a sole system which allows plantarflexion and dorsiflexion of the ankle in the gait; provides a mechanical advantage through articulation of the forefoot to stimulate an upward plantar moment force during toe-off; and increases the distance per step without altering the stride pattern.